Abstract: Considering the influence of contact surface roughness, material characteristics and other factors on the contact stress of gears, the fractal contact model of double-involute gear was established which based on the fractal theory and the classical Hertz contact theory. In this model, the main factors influencing the load and the actual contact area consisted of fractal dimension, roughness amplitude and material characteristic parameters. Theoretical calculation showed that when the fractal dimension was constant, the real contact area increased with the increase of load. When the load was constant, the contact area decreasesd with the increase of roughness amplitude. With the increase of the material characteristic parameter value, the bearing capacity of the soft material wheel tooth was enhanced to some extent, while the critical area of the micro-convex body from elastic deformation to plastic deformation was reduced. Through the comparison of two methods including fractal contact model and finite element model for calculating tooth contact stress of double involute gear teeth, the results demonstrate the effectiveness of using fractal contact model to calculate contact stress of double involute gear.